BWS 64bit Plugin Host have High CPU when using Multicore and/or HQ Mode with "some" presets in Bazille.

Bazille is a high CPU plugin, this isn't a Bitwig issue. You can disable HQ to reduce the CPU usage. There should be no need for multicore processing in Bazille, as Bitwig is already spreading processing between cores for you.

Not to be offensive to OP, but your machine is sort of old with little ram. Bazille is a hog, and I always see improvements and use multicore, but I'd consider upgrading for today's synths. I'm on i7 2.7ghz with 16gb ram mac mini and it's still a hog...

Right I suppose I didn't mention this in the answer, but I should also note, I've been using Bazille since the betas. It really just uses lots of CPU. I have a brand new MacBook Pro w/ Quad-core i7 and I can see a single instance spike CPU usage sometimes to upwards of a full core at lower latencies. For whatever reason, some presets are particularly bad for this. I typically design my own, though, and keep things reasonably simple, which usually will keep CPU usage down just fine (e.g. I'm using it for sounds, not sequences/arps in the patch). I also routinely have to disable HQ mode.

I also built an entire track out of Bazille last year for the One-Synth-Challenge. It was a CPU hog then, too... I had to restrict all patches to a single voice except for 1 chord patch to keep CPU usage down enough that my computer didn't explode...